The present invention relates generally to semiconductor fabrication and, more particularly, to an inductively coupled plasma etching apparatus and a method for controlling a chamber inner wall surface of an inductively coupled plasma etching apparatus.
In semiconductor manufacturing processes, etching processes, insulation film formation, and diffusion processes are repeatedly carried out. As is well known to those skilled in the art, there are two types of etching processes: wet etching and dry etching. Dry etching is typically implemented by using an inductively coupled plasma etching apparatus such as shown in FIG. 1.
In the inductively coupled plasma etching apparatus shown in FIG. 1, a reactant gas is first led into chamber 400 through a gas lead-in port (not shown). High frequency power is then applied from a power supply (not shown) to coil 407. Semiconductor wafer 411 is mounted on chuck 409 provided inside chamber 400. Coil 407 is held on the upper portion of the chamber by spacers 403, which are formed of an insulating material. In operation, high frequency (RF) current passing through coil 407 induces an electromagnetic current into chamber 400, and the electromagnetic current acts on the reactant gas to generate a plasma.
The plasma contains various types of radicals and the chemical reaction of the positive/negative ions is used to etch semiconductor wafer 411 itself or an insulation film formed on the wafer. During the etching process, coil 407 carries out a function that corresponds to that of the primary coil of a transformer while the plasma in chamber 400 carries out a function that corresponds to that of the secondary coil of the transformer. The reaction product generated by the etching process is discarded via exhaust port 405.
When etching one of the recently developed device materials (e.g., platinum, ruthenium, and the like), the reaction product generated may be a nonvolatile substance (e.g., RuO2). In some cases, the reaction product may adhere to wall 401 of chamber 400. If the reaction product is conductive, then the film of reaction product on wall 401 may electrically shield the electromagnetic current in the chamber. Consequently, the plasma does not strike after several wafers are etched and the etching process must be discontinued.
To avoid this problem, a method for sputtering the reaction product adhered to wall 401 by using the plasma has been developed. In the inductively coupled plasma etching apparatus shown in FIG. 1, however, the electromagnetic current induced by the RF current generates a distribution voltage having a standing wave in the vicinity of wall 401. This is problematic because it causes the deposition and sputtering of the reaction product to become non-uniform. In particular, a relatively large amount of energy is added to the plasma in the region where the amplitude of the standing wave is high. Consequently, the reaction product is excessively sputtered in this region. On the other hand, only a relatively small amount of energy is added to the plasma in the region where the amplitude of the standing wave is low, i.e., the region in the vicinity of the node of the standing wave. As a result, the reaction product is deposited in this region. As discussed above, the presence of an electrically conductive film on wall 401 is undesirable because it can electrically shield the electromagnetic current in the chamber and thereby disable the etching process.
In view of the foregoing, there is a need for an inductively coupled plasma etching apparatus that prevents substantial deposition of electrically conductive reaction products on the surface of a chamber inner wall.
Broadly speaking, the present invention provides an inductively coupled plasma etching apparatus that uniformly adds energy to the plasma in the vicinity of a wall of the chamber in which the plasma is generated.
In accordance with one aspect of the present invention, an inductively coupled plasma etching apparatus is provided. This apparatus includes a chamber for generating a plasma therein. The chamber is defined by walls of a housing. A coil for receiving high frequency (RF) power is disposed adjacent to and outside of one of the walls of the housing. A metal plate, which acts as a Faraday shield, is disposed adjacent to and outside of the wall of the housing that the coil is disposed adjacent to. The metal plate is positioned in a spaced apart relationship between the coil and the wall of the housing and has radial slits formed therein that extend transversely to the coil. A connector electrically connects the metal plate to the coil.
In one embodiment, a chuck for holding a semiconductor wafer is disposed proximate to a lower wall of the housing, and the metal plate is disposed along a surface of an upper wall of the housing. In one embodiment, the metal plate is substantially parallel to the upper wall of the housing. The metal plate preferably has a thickness in a range from about 20 xcexcm to about 10 mm, and more preferably has a thickness in a range from about 50 xcexcm to about 5 mm. In one embodiment, the metal plate has a thickness of about 1.5 mm. The connector electrically connects the metal plate to either a predetermined position of the coil or a conductor extending from an impedance matching box to the coil.
In one embodiment, the coil for receiving high frequency (RF) power disposed adjacent to and outside of the upper wall of the housing. In this embodiment, the metal plate is disposed adjacent to and outside of the upper wall of the housing and is positioned in a spaced apart relationship between the coil and the upper wall of the housing.
In one embodiment, the metal plate is secured to an underside of an attachment frame, which includes attachment spacers on a top side thereof In one embodiment, the coil is positioned between the top side of the attachment frame and a coil mounting plate, which is secured to the attachment spacers. In this embodiment, a U-shaped spacer positions the coil mounting plate, the coil, and the metal plate, and the connector electrically connects the metal plate to the coil through the U-shaped spacer.
In accordance with another aspect of the present invention, a method for controlling an inner surface of a wall defining a chamber in which a plasma is generated in an inductively coupled plasma etching apparatus is provided. In this method, a metal plate is provided between a coil for receiving high frequency (RF) power and the plasma generated in the chamber such that the metal plate does not contact the coil. The metal plate has a plurality of metal slits formed therein that extend transversely to the coil and is electrically connected to the coil. A plasma etching operation is conducted in the inductively coupled plasma etching apparatus. During the plasma etching operation, the deposition of a reaction product on an inner surface of a wall positioned between the metal plate and the plasma and the sputtering of the reaction product from the inner surface of the wall are substantially uniform so that an amount of the reaction product sufficient to disable the plasma etching operation does not accumulate on the inner surface of the wall. In one embodiment, the wall positioned between the metal plate and the plasma is an upper wall of the chamber.
The present invention advantageously prevents the deposition of electrically conductive reaction products, e.g., RuO2, on the inner surface of the wall of a chamber in an inductively coupled plasma etching apparatus. This makes it possible to plasma etch recently developed device materials, e.g., Ru, without having to stop the plasma etching operation to clean the walls of the chamber after only a few wafers have been processed.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.